STATES OF INSECTS. 273 



there is usually a suture for the purpose. The slit ra- 

 pidly extends along the head, and down the parts which 

 compose the breast, and the insect gradually withdraws 

 itself from its case. It is not, however, from the outer 

 skin merely that it has to disengage itself, but also from 

 a series of inner membranous cases, which separately in- 

 close the antennae, proboscis, feet, &c, as a glove does 

 the fingers ; and similar cases inclose the parts of the 

 perfect insect in pupas of all the other orders. This is 

 sometimes a work of difficulty, but ordinarily it is effected 

 with ease. 



Incomplete and semicomplete pupae undergo nearly the 

 same process, save that in them the body is not swathed 

 up in a common case ; and therefore they have only to 

 liberate themselves from the partial cases that envelop the 

 several parts of their body. 



In coarctate pupae, as those of Muscidtz, Syrphidce, 

 (Estridze, &c, the process is different. Their outer-case 

 is ordinarily more rigid and destitute of the sutures, 

 which in the former tribes so easily yield to a slight effort. 

 Yet in these, at the anterior end under which the head of 

 the fly lies, and from which it always issues, there is 

 commonly a sort of lid, joined by a very indistinct suture 

 to the rest, which can be pushed off, leaving a sufficient 

 opening for the egress of the insect. In the pupae of 

 many of this tribe this lid is composed of two semicir- 

 cular pieces, which can be separately removed. Many 

 species seem to be able to force off the lid of their pupa- 

 rium, by merely pushing against it with their heads : 

 but the common flesh-fly and many other Muscidce, which 

 are perhaps too feeble to effect this, or whose puparia 

 are stronger than ordinary, are furnished with a very re- 



voi.. in. T 



